Electrostatic printing



Feb. 9, 1965 E. HUTTo, JR 3,168,857

ELEcTRosTATIc PRINTING Filed May l, 1961 United States Patent O 3,163,857 ELECTROSTATIC PRN'IING Edgar Htte, Jr., Merchantviile, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed May 1, 1961, Ser. No. 106,f3 8 Claims. (Ci. 951-15) This invention relates to improved methods of electrostatic recording and more specifically to improved methods of and means `for electrophotographically preparing and utilizing transparencies.

In the art of electrophotography visible powder images may be produced on photoconductive insulating layers by producing a substantially uniform electrostatic charge on the layer, exposing the layer to a light image to produce thereon a latent electrostatic image and then applying anely-divided developer substance to the electrostatic image to produce the powder image on the layer. The photoconductive layers employed, while suitable for many purposes, are not well suited for preparing transparencies. This is due to the fact that the photoconductive layers which have been found suitable for use in electrostatic printing are too opaque. Sufficient light will not pass through them for projecting images onto a viewing screen. Therefore, to prepare a transparency using such photoconductors, it has been found necessary to transfer the electrostatic image on a photoconductive layer or a developed powder image thereon to a second transparent substrate.

Accordingly, it is a general object of this invention to provide improved methods `for producing and utilizing electrostatically prepared transparencies.

It is another object of this invention to produce powder images directly on a transparent photoconductive organic layer whereby the need for any transfer step is obviated.

A still further object of this invention is to provide improved recording-reproducing apparatus wherein tem- Cil porary powder images are produced on a transparent organic photoconductive layer and visible light images are projected therefrom.

These and other objects and advantages are accomplished in accordance with this invention by electrophotographically producing temporary powder images on an organic transparent photoconductive layer which is preferably bonded to one surface of a transparent substrate. yIt is Well known that the resistivity of a photoconductive layer will decrease with increasing temperature. The layer has a resistivity in darkness at its softening or melting temperature of at least 109 ohm-centimeters. In light it has a resistivity at least two orders of magnitude less than the dark resistivity;

An electrostatic charge image is electrophotographically produced on the ysurface of the layer. This may be accomplished, for example, by producing an overall electrostatic charge on the surface and then exposing the surface to incident radiation. Because of the diiference in the resistivity of the layer in darkness and in light the incident radiation substantially reduces or removes the charge in irradiated areas thereby forming the electrostatic image. A iinely-divided opaque developer substance is then applied to the electrostatic image to produce on the layer a temporary powder image. The layer bearing the temporary image then passes -to a projection station where light is caused to pass through the layer to provide a projected light image. After projection, the temporary image is erased byk removing the developerY substance therefrom whereupon the layer is ready for reuse.

This invention also includes apparatus for producing and projecting `the aforementioned images. The apparatus `includes means for producing a substantially uniform electrostatic charge on the surface of the thermoplastic photoconductive layer, means for producing a light image incident upon the surface of the layer, and means for applying a finely-divided developer substance to the layer. An optical projection station is provided for converting the temporary powder image into a projected light image.

Other objects and advantages appear from the following detailed description and the accompanying drawings wherein:

The single ligure of the drawing is a schematic diagram in elevation of apparatus for producing and projecting temporary images on a transparent photoconductive layer in accordance with this invention.

In practicing this invention, a photoconductive insulating layer is employed which preferably has a high degree of light transmissivity. By way of illustration such a layer may be prepared from the following materials.

Example I 27.8 parts by weight of a 36% solution of polystyrene in toluene, such as a solution of Styron PS-2 produced by the Dow Chemical Co., Midland, Mich.

7 parts by weight of the leuco base of malachite green,

bis-(4,4-dimethylaminophenyl) phenyl methane 4 parts by Weight of a chlorinated paraiiin such as, Chlorowax 70, manufactured by the Diamond Alkali Co., Cleveland Ohio 2O parts by weight methyl ethyl ketone The '7 parts of the leuco base of malachite green are dissolved in the polystyrene solution. The remaining materials are made into a second solution comprising chlorinated paraiiin dissolved in the methyl ethyl ketone. The two solutions are then mixed together and coated on a suitable substrate, such as conductive glass or metallized transparent film.

A suitable substrate comprises high quality glass such as lantern slide glass having on one surface thereof a vacuum deposited conductive iilm such as tin chloride. The solution of Example I is applied to the conductive film by known techniques, such as tiow coating, dip coating or spin coating. The solvent is then evaporated from the coating on the slide to produce thereon a thin uniform photoconductive layer. When preparing a transparent slide for use in the methods of this invention, it is -preferred that a small area of the conductive film be bared of photcconductive coating to provide means for electrically contacting or grounding the conductive film.

Another suitable substrate comprises a high-melting film, for example, one sold under the trademark Mylar or Cronar. A conductive surface can be readily produced on such a lm by vacuum deposition of a metal, for example, copper or aluminum. A photoconductive layer can be readily produced on the metallized film by known methods, Vfor example, roll coating, flow coating or dip coating. Once the photoconductive layer on the metallized -ilm is dried, a highly flexible electrophotographic member is provided.

Heat may be applied to the photoconductive layer on a'metallized glass or film substrate to accelerate the drying thereof. Once dried, continued heating for from two to three minutes at a temperature of about C. will produce a faint green tint in the clear coating. When prepared in this manner, the layer on the substrate will have maximum photoconductive response to visible light of about 6300 A. and will have another response peak at about 4200 A. i

Temporary images can be produced on the layer of Example I by employing electrostatic printing techniques. One specific method includes the following steps:

(i) Electrostatic charging-With the substrate of Example l grounded or on a grounded plate, a substantially uniform electrostatic charge is applied to the layer by passing thereover a corona generating device which aleasev' includes at least one fine wire to which is applied a potential of about $5,600 volts. Some photoconductive layers are more efliciently charged with negative polarity, others with positive polarity. However, with respect to the photoconductive layers specifically described herein either polarity of charge may be employed with about equal eiiiciency. This charging step is carried out 1n darkness or in safe light to which the layer is insensitive.

(2) Exposing-With a photographic transparency resting on the layer, it is exposed for about one to three seconds to light from a 100 watt tungsten lamp spaced up to about 18 inches away to produce an electrostatic image consisting of charged areas on the layer which correspond to the dark areas of the transparency. Exposure time can be substantially decreased by increasing the light intensity. Projection exposure techniques can also be employed.

(3) Developing-A visible powder image is produced on thelayer by applying thereto a finely-divided developer substance. This developer substance will be electrostatically held on the layer in those areas which, subsequent to exposure, retain a substantial electrostatic charge. In other areas on the layers where electrostatic charge has been substantially reduced by exposure to light the developer substance will not be held. levelopment may be accomplished with a magnetic brush. Such a brush comprises a mixture of magnetic particles and developer powder particles held together in a loose mass by a magnetic field. When this loose mass is brushed across an electrostatic image, developer powder particles are extracted therefrom by the charges in the image areas to form an electrostatically held powder image. Magnetic brush development is more fully described in U.S. Patent 2,874,063, to Harold G. Greig. In thealternative a loose powder image may be produced on the photoconductive layer by applying thereto a liquid developer composition. Such a composition comprises electroscopic developerparticles dispersed in an insulating liquid. When applied to an electrostatic image, developer particles are extracted Vfrom the liquid and are electrostatically held in image areas. Liquid developer compositions and methods of applying them to electrostatic images are described by K. A. Metcalfe and R. J. Wright in .Xerographyj Journal of the Oil and Colour Chemists Association, November 1956, volume 39, No. ll, London, England.

With the foregoing method of this invention and em- Y ploying a conductive glass slide coated with a transparent organic photoconductive material an excellent temporary transparencyl can be prepared in a few seconds for use in anordinary slide projector. For use in continuous reproducing apparatus'it is preferred to employ a flexible transparent metallized lm instead of the glass slide.

Themethods of this invention may be embodied in an apparatus 'such as that illustrated in FIG. 1. As shown inthe iigure an endless belt 1l is carried on four rollers 13,-V 15, `17 and 19. One or more of these rollers, for example, roller 13, may be driven by any suitable means, such as motor 14, to transport the belt 1l in the direction of the arrow 21.V The endless belt El preferably comprises a suitable substrate, such as a copper coated, or aluminized transparent film 23 on which a transparent photoconductive layer 25, such as that described in Example I, has been laid down.

A substantially uniform electrostatic charge is produced on the'photoconductive layer 25 as it passes under a Vcorona generating source 28. This source 23 may comprise an arraylof tine parallel wires 27 supported in a shield 29. The wires 27 are connected to a high voltage source 31 and $5000 or more volts are applied to the wires 27 to generate thereby corona for charging the photoconductive layer 425. Charging will be enhanced if, during generation of corona, the metallized 23 is at ground potential. rl`his can be easily accomplished by maintaining in contact with the exposed surface of the photoconductive layer 25 a grounded conductive roller 33. F or best results, the conductive roller should be close to the wires 27. A spacing of 3A inch or less from the nearest wires 27 will provide good results. If desired, the conductive roller 33 and the shield 27 can comprise an integrated structure both being maintained at ground potential. In the alternative a strip along one edge of the transparent iilm 23 can be bare of the photoconductive layer 25. In this instance a grounded conductive wheel replaces the conductive roller 33 and is maintained in conductive contact with the bared strip of the transparent lm 23.

The photoconductive layer 25 next passes to an exposure station where it is exposed to a light image from a cathode ray tube 34, for example, the light image from a flying spot scanner coupled to a suitable receiver 35. ln the alternative the required exposure can be provided by employing an ordinary light image projector in place of the scanner and receiver 35. The electrostatic charge in all areas of the photoconductive layer struck by light is substantially reduced or dissipated. In this way, a latent electrostatic image is formed on the photoconductive layer 25.

Next, electroscopic developer powder is applied to the electrostatic image on the layer 25. Apparatus for this purpose may comprise, for example, a magnetic structure 37 for providin0 a rotating magnetic brush 38. The structure 37 rotates in a container 39 holding a supply of developer powder 40. As the structure 37 rotates in the container 39, it picks up developer powder from a supply 40 thereof and applies it to the electrostatic image on the layer 25. A suitable rotating magnetic brush structure is described in greater detail in U.S. Patent 2,890,968, to E. C. Giaimo, lr. issued lune 16, 1959.

Once the powder image is produced on the endless belt ll it is passed to a projector 45. This projector includes, for example, a point light source 47, a condensing lens 5l and a projection lens 55. In the projector 45 light passing through a photoconductive layer 25 causes a visible light image to be projected onto a viewing screen 57. Y

Once Ythe powder image on the photoconductive layer 215 has served its purpose in the projector z5 it is removed from the layer 25. This may be conveniently accomplished by a brush cleaning structure 59. This brush cleaning structure may include a rotating librous brush 6l which rotates in Contact with the photoconductive layer 25 and removes the developer powderA therefroml Developer powder is stripped from the rotary brush 61 by means or" suction through an exhaust port 63. In most instances with the photoconductive layers specically described herein, light exposure will not reduce the electrostatic charges in exposed areas to ground potential but will leave a suiiiciently strong remnant charge in such areas that the powder image previously applied may bedimcult to remove from the photoconductive layer 25. Any such diiculty can be obviated by providing adjacent the rotating brush 61 a corona charging element 65 biased to oiliset any charges remaining on the photoconductive layer 25. Brush cleaning may be further enhanced by providing another corona generating source 67 adjacent the brush 6l. Apparatus of this type for removing powder from an insulating layer is more fully described in U.S. Patent 2,752,271, to L. E. Walkup et al., issued June 26, 1956. With respect to reducing remnant charges Y to thereby facilitatel powder removal, it is also convenient to heat the photoconductive `layersspeciiied herein. A temperature of from 30 to 40 C. will quickly remove any remnant charge and can be provided for by constructing the roller 17 as a heated roller. In applying heat to the i photoconductive' layer 25 inV this manner it is important that it be not heated to its softening temperature whereupon developer powder particles might become fused to the layer. Hence, the heating of the layer should be regulated to maintain the temperature of the :layer 25 to some point below its softening point.

Once the powder image has been removed, the endless belt 11 is ready to be recycled to produce another projected image.

In operating the device of FIG. l, movement of the endless belt 11 is desirably controlledby a start-stop cycling means 71. Such control is desirable in the case Where images projected onto the screen 57 are viewed for different periods of time than those required for producing the electrostatic image. The drive motor 14 provides frame by frame movement of the endless belt 11. During such movement, the endless belt 11 passes under the charging wires 27 and the photoconductive layer 25 becomes electrostatically charged. Since this layer 25 is a good insulator in darkness, it will retain its charge until struck by light from the projector 35.

Under control of the cycling means 61 the endless belt 11 is vstopped during exposure to a light image from the cathode ray tube 34. During this exposure, an image being viewed on the screen 57 may be retained for a time in excess of that required for complete exposure of the frame which is at rest under the projector 35. To prevent over-exposure, the cycling means 61 is coupled to a switch 72 in the control circuit of the cathode ray tube 34.

Once the electrostatic image is produced on the layer 25 it is then cycled past the developer structure 37 to the projector 4S and thence past the brush cleaner structure 59.

In lieu of the combination of resinous materials, polystyrene and chlorinated paraffin, set forth in Example I, many other resinous materials or combinations thereof may be employed in the thermoplastic photoconductive layers described herein. Suitable resinous materials include the following:

(l) Chlorinated paraflins, such as Chlorowax 70, Diamond Alkali Co., Cleveland, Ohio.

(2) Polyvinyl chloride (3) Polyvinyl'chloride copolymers, such as Vinylite VAGH, 91% vinyl chloride, 3% vinyl acetate, and

6% vinyl alcohol VYCM 91% vinyl chloride and 9% vinyl acetate VMCH 86% vinyl chloride, 13% vinyl acetate, and

1% dibasic acid (4) Polystyrene (5) Styrene butadiene copolymers such as Pliolite S-5,

Various combinations cfvresinous materials can be ernployed to provide enhanced4 iiexibility in the thermoplastic layers. For example, mixtures of polyvinyl chloride with chlorinated parains or hydrocarbon terpene resins will provide highly flexible layers.

To provide a substantially transparent photoconductive layer a dye-intermediate isselccted which is soluble in the selected resin. The leuco baseof malachite green set forth in Example I is only one of a large class of suitable dye intermediates.

Cil

6 It has the formula:

CH3 l CH3 I ons n CH3 In generahthe suitable dye intermediates have the basic formula:

wherein R1 and R2 are selected from the class consisting of monoalkylamino, di-alkylamino, mono-arylamino, and allcylarylamino; X is selected vfrom the class consisting of wherein R3 is selected from the class consisting of H, OH, CH3, OCHg, R1 and wherein R4 and R5 are selected from the class consisting of H, OH, CH3 and OCI-I3; and Y is H except when X-f-Y is double bonded oxygen.

Other suitable dye intermediates which conform to the above basic formula include the following:

(2) The leuco base of chrystal violet, tris-('4,4,4di methylaxninophenyl) methane.

dimethylaminophenyl) 4 hydroxyphenyl methane (IDH (5) Bis-(4,4dimethylaminophenyl) methane CH3 H CH3 CH3 H \C H3 (6) 4,4bis(dimethylamino) benzophenone lers ketone) CH) i CH3 (Mich- (7) Bis (4,4'-dimethy1aminopheny1) 4-t01y1 methane (8) Bis-(4,4 ethyl-benzylaminophenyl) phenyl methalle (9) Bis (4,4', dimethylaminophenyl) 2,4 dihydroxyphenyl methane.

CH3 Y /CH3 /NGJ-@IR CH3 H CH3 (10) Bis (4,4' morpholinophenyl) phenyl methane.

( 1 1 Tris- (4,4,4"-phenylaminophenyl) methane.

(12) Bis-(4,4-ethylpheny1amno phenyl) phenyl meth- (13) Bis-(4,4-methy1aminopheny1) 4"-toly1 methane.

l? i il (14) Bis (4,4-dimethy1aminophehy1)-2", 4"-dimethoxyphenyl methane.

(16) Bis (4,4 phenylaminophenyl)-4-ethy1aminophenyl methane.

(PHS N l (17) Bis (4,4-methylaminopheny1)-4"hydroxypheny1 mthane. Y

(18) Bis (4,4'-methylaminophenyl)-4-methoxyphen y1 methane.

A(19) Bis-(4,42methy1aminophehy1) 4"-t0ly1 methane.

(IDH

H It

(23) 4,4bis(ethyl-benzylarnino) benzophenone.

C 2H5 (I) C zHs l -Q-N C H2 (24) 4,4-bis-(ethyl-phenylamino) benzophenone.

C2H5 C2H5 (26) Tris- (4,4,4-ethylphenylan1inophenyl methane.

Photoconductive compositions are conveniently prepared, for example, by dissolving a quantity of the resinous material in a suitable solvent such as, for example, methyl ethyl ketone, toluene or mixtures thereof and, when the resinous material is completely dissolved, adding to the Solution a quantity of the dye intermediate. The proportion of dye intermediate to resinous material may vary over a wide range. The choice of resinous material as Well as the dye intermediate can change the optimum ratio for a given use. In many instances, it is desirable that a photoconductve layer or coating be as transparent as possible. For such purposes 0.8 part by weight or less of dye intermediate Afor each part by weight of resinous material can be employed. For some purposes, the color of a photoconductive lm or coating may not be of major concern. For such purposes, up to 1.4 parts by Weight or more of dye intermediate for each part-by Weight of resinous material may be employed. The solubility of a particular dye intermediate in a particular resin should also be taken into consideration. In some instances, if a solution is prepared containing too much dye intermediate the excess thereof Will, upon drying, crystallize out of solution which generally is undesirable.

Further illustrations of compositions which can be used to form transparent photoconductive layers exhibiting thermoplastic properties which are useful in the same manner as described in connection with Example I include the following solutions:

as, for example, Pliolite S-SB by the Goodyear Tire and Rubber Co., Akron, Ohio.

dissolved in 42.0 parts by Weight of methyl ethyl ketone.

A layer made from this solution has a softening temperature of about 55 to 57 C.

Example III 2.5 parts by weight of bis-(4,4dimethylaminophenyl) phenyl methane and 5.0 parts by weight of styrene-butadiene copolymer (Pliolite S-SD) dissolved in 42.0 parts by Weight of methyl ethyl ketone.

A layer made from this solution has a softening temperature of about 5 6 to 58 C.

Example IV 1.5 parts by Weight of bis-(4,4'-dimethyl-aminophenyl) phenyl methane and 5.0 parts by weight of styrene-butadiene copolymer (Pliolite S-S) dissolved in 42.0 parts by weight of methyl ethyl ketone.

A layer made from this solution has a softening point of about 54 to 56 C.

l Example V 1.0 part by weight of tris-(4,4,4dimethylaminophenyl) methane and dissolved in 42.0 parts by Weight of methyl ethyl ketone.

l. l A layer made from this solution has a softening point of about 85 to 87 C.

Example Vl 1.0 part by weight of tris-(4,4,4"-dimethyl-aminophenyl) methane and 5.0 parts by weight of a hydrocarbon resin such as, for example, Piccotex P-l20, Pennsylvania Industrial Chemical Corp., Clairton, Pa.

and

1.6 parts by weight of a polyvinyl chloride copolymer such as, for example, GEON 400X-1l0, B.F. Goodrich Chemical Co., Akron, Ohio dissolved in 50.6 parts by weight of methyl ethyl ketone.

A layer made from this solution has a softening point of about 50 to 52 C.

Y Example VII y 2.5 parts by weight of bis-(4,4dimethyl-aminophenyl) phenyl methane and 5.0 parts by weight of a high styrene copolymer such as,

for example, Marbon-9200 LLV, Marbon Chemical Co., a division of Borg-Warner Corp., Gary, Indiana.

and

1.2 parts by weight of a vinyl chloride copolymer such as, for example, Vinylite VYCM, Union Carbide Plastics Co., a division of Union Carbide Corp., New York, New York dissolved in Y 72.0 parts by Weight of methyl ethyl ketone.

' vand 520 parts by weight of a'high styrene copolymer Y(Marbon M-iioo TMV) and 1.6 parts by weight of a polyvinyl chloride copolymer (GEON 100K-'110) Y dissolved in y 50.0 parts by weight of methyl ethyl ketone.

A layer made from this solution has a softening point of about 48 to 50 C.

Example 1X 1.0 part by Weight of bis-(4,4-dimethylfaminophenyl) phenyl methane p and 5.0 parts by weight yof a lhydrocarbon resin (Piccotex `P-100) f i i and 1.6p'arts by weighty of a vinyl chloride copolymer (Vinylte VMCH) l Y dissolved in Example X 1.0 part by weight of tris-(4,4,4"-dimethyl-aminophenyl) methane and 5.0 parts by weight of a polystyrene resin such as, for

example, Styron PS-2, The Dow Chemical Co., Midland, Michigan and 1.6 parts by weight of a vinyl chloride copolymer (Vinylite VMCH) dissolved in 5 0.0 parts by weight of methyl ethyl ketone.

A layer made from this solution has a softening point of about 52 C.

Example XI 1.0 part by weight of tris-(4,4,4"-dimethyl-aminophenyl) methane and 5.0 parts by Weight of polystyrene resin (Styron PS-Z) and 1.6 parts by Weight of polyvinyl chloride copolymer (GEON 4GOX-ll0) dissolved in 50.0 parts by Weight of methyl ethyl ketone.

1.0 part by weight of tris-(4,4,4"-dimethyl-aminophenyl) methane and 5.0 parts by weight of a hydrocarbon resin (Piccotex and 1.6 parts by weight of a vinyl chloride copolymer (Vinylite VMCH) dissolved in Y 50.0 parts by weight of methyl ethyl ketone.

A layer made from this solution has a softening point of about 63 to 65 C.

Various modifying agents may be added to the foregoing compositions to vary the physical properties or appearance thereof provided they do not interfere with the electrical properties. Flexibility can be enhanced, for example, by including in a composition, such as that of Example I, a small amount of a plasticizer, such as, for example, tticresyl phosphate, butyl phthalylbutyl-glycolate, trs-(2,3-dibromo-propyl) phosphate, or di-(2-ethylhexyl) phthalate. Such a composition can be coated on a exible substrate or can be formed into self-supporting flexible lms. A self-supporting ilm may be produced by flow-coating a mirror-huish metal plate with the composition to form a photoconductive coating on the plate. The coating is then physically stripped from the plate and thus provides a self-supporting photoconductive hlm. Additional solvents can also be added, such as, for example, toluene to produce thev desired coating thickness of the dry nished thermoplastic photoconductiVe-layer.

When a composition is prepared wherein a dye intermediate is dissolved in a non-halogenated resin', enhanced Many of the compositions contemplated herein, when coated on a substrate or formed into a film, may have a tendency to form color which may be undesirable under some circumstances. Color formation in a film or coating can be substantially retarded by including in the compositions a small amount of stabilizer for the dye intermediate thereof. A specic example of a suitable stabilizer is one having the formula (C8H17)2Sn(S-CH2COOC8H17)2 (Thermolite 20, Metal and Therrnit Corp., Rahway, Nl). Other materials such as pyrocatechol, 2-hydroXy-4-methoxy benzophenone, and 2,2-dihydroxy4-methoxy benzophenone may also be used. Some compositions including such a stabilizer will remain substantially colorless for a considerable time unless subjected to` intense ultra-violet radiation.

What is claimed is:

l. Reproduction apparatus comprising a substantially transparent photoconductive insulating layer of organic material, means for applying a substantially uniform electrostatic charge to said layer, means for exposing said layer to a radiation image, means for applying a finely divided developer substance to said layer to produce thereon a visible image and means for projecting light through said layer for producing a projected light image from said visible image.

2. Reproduction apparatus comprising a substantially transparent photoconductive insulating layer of organic material means for transporting said layer along a predetermined path, means for applying a substantially uniform electrostatic charge to said layer, means for exposing said layer to a radiation image, means for applying iinely-divded developer material to said layer to produce thereon an electrostatically held visible image, and means for projecting light through said layer for producing a projected light image from said visible image.

3. Reproduction apparatus comprising a substantially transparent photoconductive insulating-layer of organic material means for transporting said layer along a predetermined path, means for applying a substantially uniform electrostatic charge to said layer, means for exposing said layer to a radiation image, means for applying finely-divided developer material to said layer to produce thereon an electrostatically held visible image, means for projecting light through said layer for producing a projected light `image from said visible image, and means for removing said visible image from said web.

4. Reproduction apparatus comprising a layer of substantially transparent photoconductive material having a resistivity in darkness of at least 109 ohm-centimeters and a resistivity when irradiated of at least two orders of magnitude less than said resistivity in darkness, means for K applying a substantially uniform electrostatic charge onto said layer, means for exposing said layer to a light image,

means for applying finely-divided developer substance to said layer to produce thereon a visible image and means for projecting light through said layer to produce a projected light image from said visible image.

5. The apparatus of clain` 6 wherein said layer comprises an endless loop and said apparatus includes means for removing said visible image from said layer.

6. Reproduction apparatus comprising a transparent endless belt having thereon a layer of substantially transparent photoconductive material having a resistivity in darkness of at least 109 ohm-centimeters and a resistivity when irradiated of at least two orders of magnitude less than said resistivity in darkness, corona generating means for applying a substantially uniform electrostatic charge to said layer, cathode ray tube means for exposing said layer to a light image, developer means for applying finelydivided developer substance to said layer to produce thereon a visible image, means for projecting light through said layer to produce a projected light image from said visible image and means for removing said visible image from said layer.

7. A method of image reproduction using a transparent photoconductive layer having a resistivity in darkness of at least 109 ohm-centimeters and a resistivity in light of at least two orders of magnitude less than said resistivity in darkness; said method comprising the steps of producing a substantially uniform electrostatic charge on said layer, exposing said layer to a light image, developing a visible image on said layer by applying thereto an opaque iinely-divided developer substance and projecting light through said layer to produce a projected light image from said visi-ble image.

8. Reproduction apparatus comprising an elongated transparent member at least a surface thereof comprising an organic resinous material having dissolved therein a dye intermediate, said layer having a resistivity in darkness of at least 109 ohm-centimeters and a resistivity when irradiated of at least two orders of magnitude less than said resistivity in darkness, means for applying a substantially uniform electrostatic charge to said layer, means for exposing said layer to a radiation image, means for applying a finely-divided developer substance to said layer to produce thereon a visible image and means for projecting light through said layer for producing a projected light image from said visible image.

References Cited by the Examiner UNITED STATES PATENTS 2,996,573 8/61 Barnes 178-6 X 3,051,044 8/62 McNaney 88-24 3,071,645 l/63 McNaney 95-1 X FOREIGN PATENTS 203,907 1l/56 Australia. 723,534 2/55 Great Britain.

EVON C. BLUNK, Primary Examiner. 

8. REPRODUCTION APPARATUS COMPRISING AN ELONGATED TRANSPARENT MEMBER AT LEAST A SURFACE THEREOF COMPRISING AN ORGANIC RESINOUS MATERIAL HAVING DISSOLVED THEREIN A DYE INTERMEDATE, SAID LAYER HAVING A RESISTIVITY IN DARKNESS OF AT LEAST TWO ORDERS OF MAGNITUDE LESS THAN IRRADIATED OF AT LEAST TWO ORDERS OF MAGNITUDE LESS THAN SAID RESISITIVITY IN DARKNESS, MEANS FOR APPLYING A SUBSTANTIALLY UNIFORM ELECTROSTRACTRIC CHARGE TO SAID LAYER, MEANS FOR EXPOSING SAID LAYER TO A RADIATION IMAGE, MEANS FOR APPLYING A FINELY-DIVIDED DEVELOPER SUBSTANCE TO SAID LAYER TO PRODUCE THEREON A VISIBLE IMAGE AND MEANS FOR PROJECTING LIGHT THROUGH SAID LAYER FPR PRODUCING A PROJECTED LIGHT IMAGE FROM SAID VISIBILE IMAGE. 